Two fundamentally different processes are known for seed formation on nonconductive substrates. One process starts with a solution containing colloidal metal particles, and deposits these particles as seeds directly on the substrate surface.
The other process contains the metal in the form of a soluble compound, and the metal is first deposited onto the surface in this form. The deposited metal compound is then reduced in a separate reduction step, and the metal seeds are formed directly on the surface.
One disadvantage of the known methods, however, is that with a two-stage process using a compound such as palladium chloride as the precious metal salt and tin (II) chloride, for instance, as the reducing agent, one can only activate unlaminated (i.e., free of copper metal) substrate material; otherwise, the precious metal will precipitate on (become cemented to) the copper laminate.
Simple metal salts and monomeric metal complexes also do not adsorb particularly well on many materials; or they adsorb sufficiently well only in solutions with high concentrations of the metal compound. Yet adsorbates applied to a surface in this way desorb very easily (e.g., in rinsing operations) and so do not adhere very strongly to surfaces.
Activation solutions which contain both the precious metal salt and the reducing agent (so-called colloidal activators), however, are highly sensitive to foreign ions and other contaminants, which leads to irreversible coagulation of the precious metal. Moreover, such activation solutions in which tin (II) compounds act as both reducing agent and protective colloid are unstable in comparison to oxidation by means of atmospheric oxygen, and require a continual, measured addition of the reducing agent.
These activation solutions also have the disadvantage of working at strongly acidic pH values. In the case of multiple layers, this frequently results in damage to the black/brown oxide layer in the area of the boreholes, and thus to the so-called red ring phenomenon.
All activator solutions used up to now in industrial applications share the disadvantage of working only in a rather small pH range; therefore, they require expensive controls and monitoring.